1. Field of the Invention
The present invention relates in general to a toner resin composition and toner used in electrophotography and such, and more particularly to a toner resin composition and toner used in the so-called dry developing method for developing electrostatic charge images.
2. The Prior Art
The dry developing method is widely used to develop electrostatic charge images in electrophotography. In the dry developing method, toner is usually electrified by means of friction with iron powder, glass beads, etc., which are called carriers, and then attached to electrostatic latent images on the photosensitive matter due to electrical attraction, transferred to the paper sheet, and then fixed by heating rollers and such to form permanent visible images.
For the fixing process, the heating roller method is widely used in which the toner images on said sheet are pressed onto the surface of the heating roller, which has a toner-separating material formed on its surface, as the sheet goes through.
In the heating roller method, a toner resin composition which can be fixed at a lower temperature is desirable so as to improve cost efficiency, including power consumption, and increase the copying speed.
Toner resins which contain low molecular weight or low viscosity ethylene-type wax for improved fixability and anti-offset properties have been disclosed (Japanese unexamined patent publication Tokkai Hei 7-36218 and Tokkai Hei 8-114942).
However, they have a problem in that the shelf stability is poor due to the use of the ethylene-type wax.
Regarding shelf stability, it is known that the dispersibility of the low-melting-point crystalline compound present in the toner significantly affects the toner performance. Many patent applications have already been filed pertaining to the dispersion of the separability agent in toner (Tokkai Hei 9-211889, Tokkai Hei 2-27363, Tokkai Hei 3-296067, Tokkai Hei 4-69664, Tokkai Hei 9-288370, Tokkai Hei 9-288371, Tokkai Hei 9-288372, etc.). However, these methods only control the melt-kneading conditions at the time of making toner and their effect on dispersing the separability agent is not sufficient.
That is, when a toner resin composition with a low-melting-point crystalline compound whose dispersion is not controlled is tonerized under certain kneading conditions, the dispersion becomes somewhat finer, but there is a problem in that the distribution of dispersion particle size is wide, making it impossible to obtain toner with a homogeneous dispersion particle size. Tokkai Hei 6-175396 discloses a method to control the dispersion by grafting styrene-type monomers to polyethylene wax to control the dispersion; however, the degree of crystallization of the polyethylene wax was reduced due to the grafting and the shelf stability became poor, and therefore the basic performance of the toner was not satisfactory.
The present invention solves the aforementioned problem and its object is to provide a toner resin composition with superior fixability, anti-offset properties and shelf stability, as well as a toner which uses said toner resin composition.